1. Field of the Invention
The present invention relates to an optical pickup for use in an optical disk device which records information on a recording surface of an optical disk and/or reproduces information recorded thereon.
2. Description of the Related Art
As correction means of spherical aberration for an optical disk, there is known means for correcting spherical aberration by moving a lens in an optical axis direction.
For example, Japanese Patent Application Laid-Open No. 2006-155839 discloses a configuration in which motor's rotating motion is converted into linear motion in a thrust direction and both a lens holder which abuts on a nut and a lens which is supported by and fixed to a lens holder are moved in an optical axis direction, by a screw mechanism which is combined by a lead screw formed on a motor rotation shaft and a nut engaged with the lead screw. As described above, in the configuration which obtains linear motion in the thrust direction by the screw mechanism, a backlash of the motor rotation shaft in the thrust direction can make a cause of vibration. In Japanese Patent Application Laid-Open No. 2006-155839, preload is exerted by a coil spring to bring the lens holder into contact with the nut. The preload is exerted in the order corresponding to the nut, the lead screw engaged with the nut, and the motor rotation shaft which fixes the lead screw, to bring the motor rotation shaft into contact with a thrust bearing provided at one end of the motor rotation shaft. As described above, there is the configuration that suppresses the backlash in the thrust direction by the preload.
FIG. 1 in Japanese Patent Application Publication No. 60-11536 discloses a configuration in which, in a mechanism that decelerates rotational speed of a motor rotation shaft by a worm gear, an adjustment screw is assembled at a tip end position of the motor rotation shaft; thrust adjustment is made by the adjustment screw; and then, the adjustment screw is fixed by the nut. In such configuration, an amount of movement of the motor rotation shaft in a thrust direction can be adjusted without exerting preload, and therefore, a backlash which makes a cause of vibration can be reduced.
In addition, Japanese Patent Application Laid-Open No. 2001-330027 discloses a configuration which can implement thrust adjustment at any time after assembling by providing display means for displaying an amount of movement of an adjustment screw in an axial direction of a rotation shaft.
In the thus configured optical pickup, there is a case that, after the nut and the lens holder abut on a stopper provided to control the movement in the thrust direction and stop, the nut and the lens holder will not move even if driven in a reverse direction. This is caused by that, when the nut and the lens holder stop by the stopper, the motor rotation shaft moves in the thrust direction by a reaction force from the stopper and a rotor mounted to the motor rotation shaft come in contact with a side surface in a motor case due to the movement, and consequently, a large frictional force is generated.
With respect to the above problems, in a configuration disclosed in Japanese Patent Application Laid-Open No. 2006-155839, it is possible to avoid that the motor rotor comes in contact with the side surface in the motor case, by increasing the preload of the coil spring to resist the reaction force from the stopper and to suppress the movement of the motor rotation shaft in the thrust direction. However, the preload of the coil spring continues to exert on each part during usual operation when reaction force from the stopper is not generated, and therefore, there is a possibility that movement in a reverse direction against the preload becomes difficult and there arise problems such as an increase in slide load and mechanical wear in a slide member such as a thrust bearing.
Meanwhile, Japanese Patent Application Publication No. 60-11536 and Japanese Patent Application Laid-Open No. 2001-330027 disclose the configuration in which the amount of movement of the motor rotation shaft in the thrust direction is adjusted by clamping the adjustment screw and contact between the motor rotor and the side surface in the motor case can be avoided. However, when the amount of movement of the motor rotation shaft in the thrust direction is set to zero, both ends of the motor rotation shaft come in contact with the adjustment screw and a thrust bearing while exerting a force thereon, and therefore, a slide resistance is generated. When a temperature rise is generated in such contact conditions, the amount of movement in the thrust direction due to an expansion of the motor rotation shaft is narrowed, and therefore, a further large slide resistance is generated. The increase in slide resistance becomes a load to the motor and leads to a lowering in output torque. On the contrary, when the amount of movement in the thrust direction is secured in order to decrease the slide resistance, the preload means is not provided in this configuration, and therefore, vibration in the thrust direction is generated. In this configuration, the amount of movement in the thrust direction needs to be strictly controlled in order to balance the reduction in slide resistance and the reduction in vibration level, and therefore, there is a possibility of a hindrance to improving production efficiency.